The solar dynamo and the convective rolls

Abstract

The most sophisticated attempts to model the convection zone have yielded results in which the angular velocity increases outwards and the largest scales of convection take the form of ‘banana cells’ aligned with the rotation axis. However, not only does the sign of the angular velocity gradient present problems for dynamo theory, but attempts to detect banana type cells have so far been unsuccessful. Although by no means conclusive, current tracer, spectropic, and radiative data all tend to support models of azimuthal rolls encircling the axis as the fundamental mode. It is shown here that convective upflows and downflows are preferentially generated along the rotation axis and thus initially the large-scale eddies may take the form of azimuthal rolls surrounding the poles. It is then shown that such a system may generate a progressive dynamo wave propagating from pole to equator. Since Parker has shown that an azimuthal magnetic toroid can generate a thermal shadow above it which suppresses its buoyancy, the corresponding temperature deficit so formed becomes the natural site for the downflow of the azimuthal rolls. Thus as the dynamo propagates towards the equator, so will the convective rolls. Finally the compatibility of the most recent helioseismology data with the azimuthal roll model is discussed.